A Methodology for Mapping Tsunami Hazards and Its Implementation for the Far Eastern Coast of the Russian Federation

Doklady Earth Sciences - Overview maps of tsunami hazards for the Far Eastern coast of the Russian Federation are created. The methodological principles of the PTHA (Probabilistic Tsunami Hazard...     

Relationship of Tsunami Intensity to Source Earthquake Magnitude as Retrieved from Historical Data

Operational prediction of near-field tsunamis in all existing Tsunami Warning Systems (TWSs) is based on fast determination of the position and size of submarine earthquakes. Exceedance of earthquake magnitude above some established threshold value, which can vary over different tsunamigenic zones, results in issuing a warning signal. Usually, a warning message has several (from 2 to 5) grades reflecting the degree of tsunami danger and sometimes contains expected wave heights at the coast. Current operational methodology is based on two main assumptions: (1) submarine earthquakes above some threshold magnitude can generate dangerous tsunamis and (2) the height of a resultant tsunami is, in general, proportional to the earthquake magnitude. While both assumptions are physically reasonable and generally correct, statistics of issued warnings are far from being satisfactory. For the last 55 years, up to 75% of warnings for regional tsunamis have turned out to be false, while each TWS has had at least a few cases of missing dangerous tsunamis. This paper presents the results of investigating the actual dependence of tsunami intensity on earthquake magnitude as it can be retrieved from historical observations and discusses the degree of correspondence of the above assumptions to real observations. Tsunami intensity, based on the Soloviev-Imamura scale is used as a measure of tsunami “size”. Its correlation with the M _s and M _w magnitudes is investigated based on historical data available for the instrumental period of observations (from 1900 to present).     

Magnitude-geographical criterion for operational tsunami prognosis: Analysis of application in 1958–2009

Re-evaluation of magnitude-geographical criterion of tsunami prediction is one of the main directions of improvement of the tsunami warning service acting on the coast of the Russian Far East. The main directions of this work are a careful analysis of the tsunami warnings issued by the service during the period of its operation (since 1958), determining of reasons for false alarms and missed warnings, delineation of tsunamigenic areas threatening the Far East coast of Russia, optimal selection of magnitude thresholds for each tsunamigenic zone, evaluation of the expected ratio between real/missed/false warnings, determination of the degree of influence of other source parameters (focus depth, source mechanism), and evaluation of probability of occurrence for nonseismic tsunamis. The present paper considers the results of operations for prediction of tsunamis from submarine earthquakes that occurred in the Kuril-Kamchatka zone, Sea of Japan, and Sea of Okhotsk during the last 52 years.     

Assessment of the tsunami hazard on the Russian coast based on a new catalogue of tsunamis in the Black Sea and the Sea of Azov

We present the results of work on the compilation of a fuller and more comprehensive historical catalogue of earthquakes and tsunamis in the basin of the Black Sea and the Sea of Azov, an area of primary importance for the Russian Federation. In the 20th century, there were no significant tsunamis in the Black Sea; therefore, its coast was not considered tsunami-prone. A systematic search for new data sources, a revision of earlier ones, and the use of new approaches to the identification of tsunamigenic events resulted in a more than doubling of the number of known tsunamigenic events in this basin, bringing it up to 50. The total length of the new tsunami catalogue reached 3000 years, which makes it the second longest after the Mediterranean tsunami catalogue (about 4000 years). Taking into account the seismotectonic features of the Black Sea region, we processed data on historical tsunamis and analyzed the geographical and temporal distributions of their sources. For all tsunamigenic events we performed a parameterization of available information about their sources and coastal manifestations, evaluated the tsunami intensity based on the Soloviev-Imamura scale, and proposed a classification of tsunami and tsunami-like water wave disturbances based on their genesis. Tsunami run-up heights, inland penetration, and damage were estimated with regard for the newly found data. Among the identified historical events, there are devastating tsunamis with run-ups of 4-5 m, sometimes up to 6-8 m, which resulted in disastrous consequences for several ancient cities (Dioscuria, Sebastopolis, Bizone, and Panticapaeum) and many coastal settlements. Expert assessments of the most tsunami-prone areas of the coasts are given.     

Numerical simulation of the action of distant tsunamis on the Russian Far East coast

Results of a numerical simulation of the action of distant tsunamis on the coast of the Russian Far East are presented. It is shown that waves generated by focuses of the strongest M9 earthquakes in the region of South Chilean coast, as well as in the region of Papua New Guinea and Solomon Islands, are most dangerous for this coast. Other tsunamigenic zones of the Pacific Ocean, by virtue of their geographical position, orientation of focuses, and absence of pronounced channels (submarine ridges) along paths of tsunami propagation are not dangerous for it even at a limit magnitude of submarine subduction earthquakes. The simulation results are compared with historical data about manifestations of distant tsunamis on the Russian Far East coast.     

Strongest tsunamis in the World Ocean and the problem of marine coastal security

We consider the problems of assessing tsunami danger for sea coasts taking into account the risk of the strongest tsunamis of seismic origin. We identify a class of particularly dangerous transoceanic events characterized by extremely high runups (up to 40–50 m) at extended coastal areas (up to 500–1000 km). In most cases these transoceanic tsunamis are caused by underwater mega-earthquakes with a magnitude of 9.0 or more occurring with a period between 200–300 and 1000–1200 years in some areas of subduction zones. The possibility of these earthquakes in subduction zones directly threatening a given coast should be taken into account in creating maps of tsunami zoning of any scale.     

The 1994 Shikotan earthquake tsunamis

The 1994 Shikotan earthquake was one of the greatest earthquakes in recent years with a magnitude ofM _s 8.0. A tsunami survey was conducted by Russian and U.S. geophysicists from October 16–30, 1994, less than two weeks after the earthquake. The survey results and a numerical hindcast simulation are reported. Tsunami focusing effect at locations supposedly sheltered by the island chain is discussed. Based on the obtained data, tsunamis which attacked Shikotan Island are characterized as long waves (the order of 10–20 min wave period) with a positive leading wave. Possible consequences of the positive leading wave form are discussed in relation to the observed minimal destruction of beach vegetation and relatively small transport of marine sediment onto the shore. The high-quality tide-gage record in Malokurilskaya Bay indicates the occurrence of a 53 cm subsidence at the site.     

Understanding and reducing the disaster risk of landslide-induced tsunamis: a short summary of the panel discussion in the World Tsunami Awareness Day Special Event of the Fifth World Landslide Forum

Landslides - A World Tsunami Awareness Day Special Event was held in hybrid mode on 5 November 2021, during the Fifth World Landslide Forum, in Kyoto, Japan. In this context, a panel discussion was...